This invention relates generally to food products that have been adulterated with antibiotics or other contaminants. More particularly, this invention relates to a method for reconditioning dairy products, especially milk, that have been adulterated with antibiotics or other contaminants.
Antibiotics have greatly improved the quality and duration of life because they kill or inhibit growth of primarily prokaryotic microorganisms, many of which are disease-causing agents. In addition to their use in human medicine, antibiotics are also administered to livestock at therapeutic, prophylactic, or sub-therapeutic levels. S. Levy, 50 J. Food Prot. 616 (1987). Therapeutic administration is for disease treatment, prophylactic administration is to prevent disease, and sub-therapeutic administration is for increasing feed efficiency and promoting growth. In 1983, nearly one-half of the 35 million pounds of antibiotics manufactured in the U.S. was fed to animals. W. Tindall, 40 Animal Nutrition and Health 18 (1985). The cattle, swine, and poultry industries are the largest users of antibiotics, particularly penicillins and tetracyclines. C. Burbee et al., Am. J. Agr. Econ. 966 (1985). The administration of antibiotics to animals has become so widespread that nearly 80% of poultry, 75% of swine, 60% of feed lot cattle, and 75% of dairy calves are fed antibiotics. D. Franco et al., 53 J. Food Prot. 178 (1990).
Bacteria can become resistant to antibiotics, and this resistance can occur in a short period of time after therapeutic or sub-therapeutic exposure. Therapeutic oral intake of tetracycline in humans can lead to emergence of a predominantly tetracycline-resistant coliform gastrointestinal flora within 48 hours. L. Hartley & M. Richmond, 4 Brit. J. Med. 71 (1975). Sub-therapeutic levels of tylosin fed to piglets led to 100% macrolide-resistant fecal streptococci within a few days. G. Dunny et al., Effects of Antibiotics in Animal Feed on the Antibiotic Resistance of the Gram Positive Flora of Animals and Man (New York Public Health Inst. 1978).
Antibiotic resistance in microorganisms can be transferred to other organisms, generally on plasmids. These plasmids often carry multiple drug resistance genes, thus administration of antibiotics develops resistance not only to the antibiotic being administered but to other antibiotics as well. Humans may become infected with antibiotic-resistant microorganisms by consuming meat, milk, or other animal products from animals in which the microorganisms have developed. S. Holmberg et al., 311 N. Engl. J. Med. 617 (1984); C. Ryan et al., 258 J. Am. Med. Ass'n 3269 (1987). Ironically, the humans at greatest risk may be those taking antibiotics for treatment of other conditions. S. Holmberg et al., 311 N. Engl. J. Med. 617 (1984). The Center for Disease Control estimates that 25% of the Salmonella isolated from human infections are resistant to antibiotics.
After reviewing data on drug resistance-plasmid transfer, the Food and Drug Administration (FDA) began regulating use of antibiotics in animals destined for human consumption. As of July, 1991, 23 antimicrobial agents were FDA-approved for one or more uses in livestock and poultry feeds. 33 Food Chem. News 51 (1991). The FDA requires specific withdrawal times after treatment with antibiotics for livestock prior to lactation or slaughter. For example, FDA regulations require that milk from treated cows be discarded for 96 hours following the last administration of the antibiotic. E. Seymour et al., 71 J. Dairy Sci. 2792 (1988). Further, the FDA establishes tolerance limits, the maximum legally allowable levels or concentrations of a drug or chemical in a food product at the time the milk is marketed or the animal is slaughtered. "Safe levels" are also used by the FDA as guides for deciding whether or not to prosecute. They are not binding, do not dictate any result, do not limit the FDA's discretion in any way, and do not protect milk producers from court enforcement action. For some antimicrobials, no tolerance or safe level is allowed. 21 C.F.R. .sctn. 556 (1993).
In 1991, the FDA began the National Drug Residue Milk Monitoring Program to test for various drug residues in milk. A requirement under the Pasteurized Milk Ordinance (PMO) for industry screening of all bulk milk pickup containers for .beta.-lactam antibiotic residues went into effect Jan. 1, 1992. Pasteurized Milk Ordinance, Appendix N. Further, tankers are randomly tested for the presence of other drug residues in milk, and all test results are reported to the appropriate state regulatory agency. Upon a first violation of the regulation, Grade A permits (for fluid milk) are revoked for 2 days. Upon a second violation, Grade A permits are revoked for 4 days, and upon a third violation the permit may be suspended. Pasteurized Milk Ordinance, Appendix N.
In 1993, the U.S. Department of Agriculture (USDA) instituted a drug residue monitoring program for manufacturing grade milk. This program requires that all USDA-approved dairy plants sample and test all raw milk shipments individually for .beta.-lactam drugs prior to processing. Further, each violative producer will be reported to the appropriate state regulatory agency by the plant and will be suspended from shipment until milk from subsequent milkings tests negative for drug residues. Besides nonacceptance of milk containing drug residues, additional penalties are provided for producers who ship milk testing positive for drug residues.
A survey conducted by the Milk Industry Foundation, representing 78% of the total volume of fluid Grade A milk in 1992, revealed that 1,770 tankers of milk, or about 0.09% of the total, tested positive for drug residues. Of that total, about 90% were .beta.-lactams, 4% were tetracyclines, 4% were sulfamethazine, 2% were erythromycin, and 0.2% were gentamicin. While the percentage of contaminated tankers was relatively low, individual producers may suffer significant economic effects from having antibiotics detected in their milk. The reasons for occurrence of drug residues in milk is mainly associated with errors due to hired help, insufficient knowledge about withdrawal periods, poor animal identification techniques and documentation of treated animals, and the use of medicated feeds. J. Kaneene & A. Ahl, 70 J. Dairy Sci. 2176 (1987). The PMO provides that antibiotic-adulterated milk may be reconditioned by removal of the offending antibiotics from the milk, Pasteurized Milk Ordinance, Appendix N, however there is currently no economically viable commercial method to accomplish it.
Other types of contaminants can also adulterate milk and other liquid food products, and it is desirable to remove such contaminants therefrom. Such contaminants can include bacterial cells, bacterial spores, viruses, proteins, and enzymes. Commercial methods to remove such contaminants without altering the natural composition of the milk or other liquid food product are unknown in the art.
R. Brown et al., U.S. Pat. No. 4,347,312, disclose a method akin to radioimmunoassay (RIA) for detecting the presence of penicillin in milk. Anti-penicillin antibodies are bound to a solid support. Then, a milk sample is mixed with a known quantity of horseradish peroxidase-labeled penicillin and exposed to the support. Alternatively, the support is exposed to the milk sample and the labeled penicillin consecutively. The support is rinsed and then the amount of labeled penicillin bound to the support is determined with a calorimetric substrate. Penicillin in the milk sample and the labeled penicillin compete for attachment to bound antibodies, thus the amount of penicillin in the milk sample can be determined by comparison to a standard curve. This method is effective for quantifying an antibiotic in a small, static volume of milk, but is ineffective for quantitative removal of contaminants on an industrial scale wherein an immobilized antibody is exposed to the high shear forces associated with the high flow rates of an industrial process. Also, the solid support and associated antibodies are discarded after one use, thus making the method expensive. Further, the immobilized antibody is nonspecifically oriented on the solid support such that only one antigen binding site per antibody is available for binding an antigen in milk.
Charm, U.S. Pat. No. 4,238,521, discloses a method of removing penicillin from penicillin-contaminated milk comprising the steps of contacting the penicillin-contaminated milk with a bed of activated charcoal, recycling the milk through the bed of charcoal for a sufficient period to remove the penicillin from the contaminated milk to provide a penicillin-free milk, removing particulate activated charcoal acquired during the contacting step by filtration and centrifugation, and recovering the penicillin-free milk. This method is a crude, shotgun approach and provides no specificity for removing any particular constituent of the penicillin-contaminated milk. Indeed, normal components of milk are removed by contacting the milk with activated charcoal. Further, charcoal particles contaminate the milk after being contacted by the activated charcoal, and steps must be taken to remove such particles from the penicillin-free milk. Moreover, the method is relatively slow, and the capacity for removing antibiotics is relatively low, which are disadvantages compared to the presently disclosed invention.
R. Geyer, U.S. Pat. No. 5,310,565, discloses a method of treating milk to remove antibiotics comprising heating the antibiotic-contaminated milk to a temperature sufficient to solubilize fats, contacting the heated milk with an ion exchange or adsorbent resin to produce an antibiotic-depleted milk, and collecting the antibiotic-depleted milk. This method is also relatively crude and non-specific as shown by altered mineral profiles, removal of proteins such as riboflavin, and altered pH of the antibiotic-depleted milk. These changes are also disadvantages as compared to the presently disclosed invention.
In view of the foregoing, it will be appreciated that a method for specifically removing a selected contaminant, such as an antibiotic, bacterial cell, bacterial spore, virus, enzyme, or protein, from milk or other liquid food product without altering the natural composition of the milk or other liquid food product would be a significant advancement in the art.